This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The cytochrome bc1 complex is an important target for pharmaceutical (e.g. Atovaquone, Leucascandrolide) and agricultural fungicides (azoxystrobind, kresoxym-methyl, famoxadone) These chemical affect the position of the Rieske iron-sulfur protein (RISP) in the crystals in a fashion that may reflect a catalytic switch mechanism for gating the electron transfer. We are studying the mode of binding of these inhibitors to elucidate the mechanism of the enzyme and to enable development of better inhibitors. Some of the time will also be used for testing new crstals from projects related to respiratory complex maturation, innate immunity, and signal transduction.